This invention relates to permanent magnet dc electric motor having a rotor and a stator and at least a pair of oppositely disposed main magnets. In particular, the present invention provides diverting magnets for use with the main magnets which provides a magnetic field having a very high flux density, which means high reluctance with little magnetic leakage. In particular, the present invention relates to a permanent magnet stator for a dc motor having diverting magnets which provide high reluctance at the inner periphery of the stator magnets, but which have little magnetic leakage between the interpolar space and also low magnetic leakage at the outer periphery of the stator magnets.
The present invention is based upon the free pole theory. In a permanent magnet, atoms consist of very small atomic nuclei surrounded by clouds of electrons. In some kind of atoms, there are more electrons circulating in a clockwise direction around its own axis than in a counterclockwise direction. There is then resultant rotational motions of electrons around the nucleus. Such motion of electrons constitutes a current and develops a magnetic field just as current in a coil produce a magnetic field. They are little permanent magnets with external fields just like the field of dipole. It is a well known, observed phenomenon that when two like poles of permanent magnets are facing each other, strong repulsion occurs therebetween. The flux density in the middle of two like poles seems greater than original flux density. Because of opposing magnetic fields, negative divergence occurs near the center of two like magnets. The negative divergence of magnetic pole at a point inside of the body equals the pole strength per unit volume at that point. These diverged poles are called free poles.
In the case of unlike poles which attract each other, all of the free poles are diverged to opposite sides and intensify the flux density at both ends of the magnet.
In order to design a good permanent magnet dc motor, several important design parameters should be considered. The magnetic density at the pole faces should have maximum value, and interpole magnetic leakage and magnetic leakage at the outer periphery of stator magnets should be minimum. For instance, the conventional, two pole permanent magnet dc motor has a large interpole working air gap, the greater reluctance of the long air gap reduces the total flux, and increases the magnetic leakage, and there is more leakage because there is little difference in the reluctance of the useful and the leakage path. Although the magnetic flux can be encouraged to follow a ferromagnetic path and to cross a working air gap, it cannot be confined completely thereto because of ferromagnetic material exhibit a non-linear relation between flux density B and magnetizing force H, because the saturation phenomenon. Prior art designs attempted to increase the useful flux density, and to reduce the magnetic leakage. A permanent magnet stator for reducing the magnet leakage between the main magnets is disclosed in U.S. Pat. No. 4,243,903. As illustrated in FIG. 1, this prior art has two blocking magnets 4 and 5, each producing a magnetic field opposite in direction, but equal in intensity to the magnetic field between the main magnets 1 and 2. At the vicinity of boundary areas 6, 7, 8 and 9 where two opposing poles meet together, a very high intensity magnetic flux is created. This might be good as useful reluctance for the armature, but the areas 6, 7, 8 and 9 will emit strong magnetic field through the yoke 3 as wasted magnetic leakage.
Another previous invention relating to increasing flux density and reducing magnetic leakage is disclosed in U.S. Patent No. 4,459,500, and shown in FIG. 2. A pair of auxiliary magnets 10 and 11 are mounted on the axial end surface of a pole piece 12 to reduce the magnetic flux leakage from the pole piece 12 for increased magnetic force. FIG. 2 shows the positional relationship between the pole piece 12, permanent magnets 13 and 14 and repulsive auxiliary magnets 10 and 11 which are disposed around the pole piece 12. A north seeking pole N appears on the inner surface 15 of the pole piece 12. Because all four magnets are facing each other, all the diverged magnetic poles are diverged toward the pole piece 12, and intensify the magnetic flux at the pole piece 12, and provide a high flux density at pole piece face 15. Despite the high flux density at the pole face 15, it has low reluctance, and a high magnetic leakage at the outer surface 16.
Therefore, it is obvious that the prior art motors increased the flux density at the cost of magnetic leakage, and the magnetic field efficiency per fixed magnet volume.